In early 1945, Vanier was visiting Paris where his father was Canadian Ambassador; he and his mother went to assist survivors of Nazi concentration camps. Seeing the emaciated victims, their faces twisted with fear and anguish, was a profoundly moving encounter for him, which he never forgot. Shortly thereafter, at age seventeen, with World War II still raging, he served with the Royal Navy and then with the Royal Canadian Navy. In 1947 as a midshipman, Vanier accompanied the Royal Family on their tour of South Africa aboard HMS Vanguard.

In 1964, through Vanier's friendship with a priest named Father Thomas Philippe, he became aware of the plight of thousands of people institutionalised with developmental disabilities. Jean Vanier invited two men, Raphael Simi and Philippe Seux, to leave the institutions where they resided and live with him in Trosly-Breuil, France. He also assisted in institution schools.

He expanded his efforts and established L'Arche at Trosly-Breuil, a community for people with disabilities to live with those who cared for them. He helped develop such communities in other places around the world. Until the late 1990s, Jean Vanier carried the responsibility for L'Arche in Trosly-Breuil in France, and for the International Federation of L'Arche. He stepped down to spend more time counseling, encouraging and accompanying the people who come to live in L'Arche as assistants to those with disabilities.

In 1968, Jean Vanier gave a Faith and Sharing retreat in Marylake, Ontario the first of a movement of retreats where people from many walks of life are welcome.[5] The retreats continue today as part of the Faith and Sharing Federation.[6] As of 2013, there are 13 communities in North America that organize annual retreats and days of prayer.[7] Faith and Sharing member Bill Clark, SJ explains: "There is then a two-fold movement in Faith and Sharing: an inward movement towards God hidden in the depths of our own vulnerability, and an outward movement towards our brothers and sisters, especially those who are more poor and in need." [5] The organization's records are housed at the John M. Kelly Library, University of St. Michael's College.[8]

In 1971, he co-founded Faith and Light with Marie Helene Mathieu. It is an international movement of forums for people with developmental disabilities, their family and friends. Today there are over 1,800 Faith and Light communities in 80 countries around the world.[4]

Vanier still makes his home in the original L'Arche community of Trosly-Breuil, France. He travels widely, visiting other L'Arche communities, encouraging projects for new communities, and giving lectures and retreats.

In March 2015 Vanier was awarded the Templeton Prize in recognition of his advocacy for people with disabilities and his contributions to a broader exploration of helping the weak and vulnerable.[13][14]